1. Technical Field
This Patent Document relates generally to hybrid or composite amplifier/regulator architectures that combine a switched mode converter and a linear amplifier, also referred to as linear assisted switched mode or a switched mode assisted linear architectures.
2. Related Art
A hybrid regulator includes a switched mode converter (or switched converter) and a linear amplifier coupled in parallel at a power output node, and cooperatively controlled to supply regulated load voltage. In such hybrid regulators, the higher bandwidth but less efficient linear amplifier supplies the higher frequency content of the output power, while the more efficient but lower bandwidth switched converter provides the lower frequency content.
One application for a hybrid regulator is as an envelope modulated power supply for an RF (radio frequency) power amplifier (PA). Envelope modulation/tracking improves power amplification efficiency for high peak-to-average power ratio (PAR) signals such as typical of mobile RF communications—envelope modulated regulators dynamically control the RF PA supply voltage, tracking PA output power variations/requirements.
Design parameters for an envelope modulated/tracking power supply include noise, distortion and bandwidth. Noise and distortion generated by the envelope modulator and injected into the PA supply pin will transfer to the PA output spectrum. For hybrid regulator architectures, a significant noise source is switching noise from the switched mode converter, and an important design criteria is to reduce small signal output impedance of the linear amplifier over the operational bandwidth of the envelope modulator (the output impedance bandwidth).
Hybrid regulators can be configured with the linear amplifier AC coupled to the power output node, such that the linear amplifier is only required to supply AC content of the bad voltage. DC average voltage at the output of the regulator is maintained on the AC coupling (DC-decoupling) capacitor.
While this Background information is presented in the context of regulated power supplies for power amplifier applications, this Patent Document is not limited to such applications, but is more generally directed to hybrid architectures that include a switched mode converter and a linear amplifier.